1. Field of the Invention
The invention relates generally to an improved optical imaging head for use in transferring images to a recording medium, and more particularly, to a dual telecentric, high powered optical imaging head operating with zero order diffractive radiation in an external drum imagesetter.
2. Description of the Prior Art
With any image to be printed in the printing industry, a typical first step in the overall process is prepress operations, that is, to transform digital information representing the image of interest onto a light or thermal sensitive medium, e.g. a printing plate, which is then used to transfer the image any number of times on a printing press. As prepress technologies have evolved, the time required to create the image has been reduced while the quality of the image has improved. Also evolving is the media used for film, plates, proofing and final production. This evolution continues to drive the requirement for a faster, higher quality, imaging system capable of imaging on many different recording media.
One method for reducing imaging time is to increase the number of beams that write on the media at any one time. There exist in the art several methods for creating multiple writing beams from a single source. These previous methods include the use of a multi-channel acousto-optical modulator (AOM), various beam splitting technologies and multi-element modulators such as digital micromirror devices (DMD.TM. trademarked by Texas Instruments), and lanthanum modified lead zirconate titanate which can be fabricated as a transmissive ferroelectric ceramic modulator, also known as PLZTs.
A new type of multi-element modulator, the grating light valve or GLV, has recently been developed for use in the field of displays by Silicon Light Machines, Inc. of Sunnyvale, Calif. This GLV is an addressable diffraction grating, formed of moving parts on the surface of a silicon chip. Each GLV pixel consists of dual-supported parallel ribbons formed of silicon nitride and coated with a reflective aluminum top layer. Several publications are incorporated herein by reference in their entirety to provide supplemental background information on grating light valves which is not essential but is helpful in appreciating the applications of the present invention. They are: "Grating Light Valve.TM. Technology: Update and Novel Applications" by D. T. Amm et al., presented at Society for Information Display Symposium, May 19, 1998, Anaheim, Calif.; "Grating Light Valve.TM. Technology for Projection Displays" by R. W. Corrigan et al., presented at the International Display Workshop, Kobe Japan, Dec. 9, 1998, Paper Number LAD5-1; "Optical Performance of the Grating Light Valve Technology" by D. T. Amm et al., presented at Photonics West-Electronic Imaging, Jan. 27, 1999, San Jose, Calif.; and "Calibration of a Scanned Linear Grating Light Valve.TM. Projection System" by R. W. Corrigan et al., presented at Society for Information Display Symposium, May 18, 1999 in San Jose, Calif.